In recent years, LEDs having superior energy saving characteristics have been spotlighted in lieu of light bulbs or fluorescent lamps. Furthermore, various structures of lighting devices using LEDs are also being proposed (for example, Patent document 1).
FIG. 9 is a sectional view illustrating an embodiment of a conventional structure of an edge-type lighting device. In the drawing, reference numeral 202 denotes a light guide plate made of a transparent material, and reference numeral 203 denotes light sources which are disposed facing each other on respective edges of the light guide plate 202 and emit light L1 into the light guide plate 202. The lighting device is configured such that light L1 that is emitted from the light source 203 and enters the light guide plate 202 is emitted from a front surface of the light guide plate 202 (see reference numeral L2). In the edge-type lighting device having the above-mentioned construction, the light sources 203 can be disposed on the edges of the light guide plate 202 rather than on a rear surface of the light guide plate 202. Therefore, the edge-type lighting device can be markedly reduced in thickness. Such an edge-type lighting device is mounted to a ceiling, a sidewall, etc. of a room or the like.
Meanwhile, a variety of structures that pertain to conventional lighting devices using light bulbs, fluorescent lamps or LEDs have been proposed (for example, Patent document 2).
FIG. 10 is a perspective view showing an embodiment of the structure of such a conventional lighting device. Reference numeral 301 denotes a light source unit which has an approximate rectangular surface and is configured such that light L2 is emitted from the rectangular surface. Reference numeral 302 denotes a frame member which is disposed at a rear surface of the light source unit 301, and reference numeral 303 denotes suspension pipes which suspend the lighting device from a ceiling.